1. Field of the Invention
The present disclosure generally relates to a variable buoyancy subsea running tool used to run a subsea transportable device, such as an internal tree cap, to a subsea tree. Typically, a subsea running tool can be manipulated using a remotely operated vehicle (“ROV”).
2. Description of the Related Art
A wellhead assembly, such as that employed on the seabed for offshore drilling and production operations may often include a “conventional” or “vertical” subsea tree used to access the well bore. The subsea tree includes a bore that may be sealed off or isolated using a subsea transportable device such as a tree cap. An ROV and a subsea running tool are sometimes used to facilitate the installation of the tree cap.
Horizontal subsea “Christmas” tree systems are often completed with an internal tree cap as a secondary barrier. Due to the nature of this operation and its related high cost, the internal tree cap has been a challenging and costly completion activity. There is a need to solve installation problems of an internal tree cap that make it risky and less profitable.
An ROV may be used to install and retrieve the tree cap in open water. But, since an internal tree cap with pressure barrier capability is very heavy with respect to the submerged weight of an ROV designed to transport the internal tree cap the heavy submerged weight may cause poor handling and maneuverability with the ROV. Installing floaters on the tree cap to offset its submerged weight may possibly help with the ROVs diminished handling and maneuverability. However, the tree cap does not provide much space on which to install floaters. One potential solution to this problem is mounting floaters on the running tool used to transport and install the internal tree cap. While this added buoyancy helps in the transport of the tree cap to the subsea tree, once the tree cap is deployed the floaters added to the running tool present a potential problem. With the running tool free from the extra weight of the tree cap, the buoyant effect of the floaters may lift the running tool to the surface without substantial control causing a potentially dangerous situation.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the issues set forth above.